An organic photosensitive drum used for a printer of an electrophotography method is manufactured by uniformly applying a photosensitive layer on an outer surface of a hollow cylinder made of metal or a conductive material. The above-described organic photosensitive drum may be classified into a single layer type and a function separated lamination type according to constitution of the photosensitive layer.
The single layer type organic photosensitive drum is manufactured by applying a lower layer having a thickness of 0.5 to 10 μm, more desirably 1 to 7 μm, on the outer surface of the hollow cylinder made of the metal or the conductive material as necessary, applying an electric charge generation transport layer containing all of an electric charge generation agent and an electric charge transport agent and having a thickness of 10 to 40 μm on the lower layer, and applying a protection layer having a thickness of 1 to 10 μm, more desirably 3 to 8 μm, as necessary on the electric charge generation transport layer. The function separated lamination type organic photosensitive drum is manufactured by applying a lower layer having a thickness of 0.5 to 10 μm, more desirably 1 to 7 μm, on the outer surface of the hollow cylinder made of the metal or the conductive material as necessary, sequentially applying an electric charge generation layer having a thickness of 0.1 to 5 μm, more desirably 0.2 to 2 μm, and an electric charge transport layer having a thickness of 10 to 40 μm on the lower layer, and applying a protection layer having a thickness of 1 to 10 μm more desirably 3 to 8 μm on the electric charge transport layer as necessary. Although a method for applying the photosensitive layer of the above-described single layer type or function separated lamination type organic photosensitive body includes a spray jet method, a ring-coating method, and an immersion coating method, the immersion coating is generally widely used in terms of uniformity and productivity of a formed layer.
FIG. 1 is a process conceptual view illustrating a photosensitive material coating method performed by a conventional general immersion method. The immersion coating method is a method in which the hollow cylinder 20 is vertically immersed into a photosensitive solution 30 and then taken out to apply and dry the photosensitive solution 30 to an outer surface of the hollow cylinder 20 in a state in which an inner surface of the hollow cylinder 20 is gripped by a gripping mechanism 120 such as a O-ring compression picker compressing an O-ring shaped elastic member to the inner surface of the hollow cylinder 20 in a mechanical method to expand an external diameter thereof or a balloon type air picker applying pneumatic pressure to a balloon shaped elastic member to be expanded. The above-described gripping mechanisms grip by closely attaching the elastic member of the gripping mechanism 20 to a portion of the inner surface of the hollow cylinder 20 and simultaneously secure inner sealing. Referring to the gripping process in a previous step of the immersion in detail, in a state in which the hollow cylinder 20 is vertically stood by a jig (not shown) inserted from a lower portion thereof, as an entire body of the gripping mechanism 120 is entered into to grip the hollow cylinder through an upper portion of the hollow cylinder 20 and then the gripping mechanism 120 is lifted, the hollow cylinder is carried out from the inserted jig.
In the above-described method, the hollow cylinder loaded on a transfer pallet and the gripping mechanism should be aligned with each other on an coaxial line at a high precision degree so that a plurality of gripping mechanisms mechanically fixed to a chuck are smoothly and respectively entered into a plurality of hollow cylinders, of which movement is restricted by the jig of the transfer pallet, vertically loaded on the transfer pallet. In particular, a coaxial line alignment error due to angular misalignment in the process of entering the gripping mechanism into the hollow cylinder is gradually deepened from an upper end to a lower end of the hollow cylinder. In detail, as the jig of the transfer pallet has an external diameter less by an appropriate difference than an internal diameter of the hollow cylinder, when the difference is great, the gripping mechanism firstly enters and a center of the hollow cylinder is moved by a gap formed by the difference to partially resolve the coaxial line misalignment. However, since initial coaxial line alignment between the gripping mechanism and the hollow cylinder is unfavorable, possibility of failure on the initial entry of the gripping mechanism increases. On the contrary, when the difference is too small, the initial coaxial line alignment between the gripping mechanism and the hollow cylinder becomes better. However, since the gap in which the center of the hollow cylinder is moved is small when the gripping mechanism enters, the coaxial misalignment caused by the angular misalignment is deepened to cause damage to the gripping mechanism and the hollow cylinder or generate a problem in which the hollow cylinder is not separated from the jig even when gripped.
Meanwhile, since in the related art, a final position at which the gripping mechanism 120 grips an inner surface of the hollow cylinder 20 includes a distance from a lower end of the hollow cylinder 20 to an upper end of the jig inserted in an upward direction, the final position is restricted to a considerably spaced position to form a considerable space from a position in which the elastic member of the gripping mechanism is closely attached to the inside of the hollow cylinder to the lower end thereof, which generates a problem that will be described later in the coating process.
In general, the photosensitive solution used in the immersion coating process is generally prepared by dissolving or diffusing a bonding agent resin or a photosensitive material into an organic solvent. Here, as the used organic solvent, toluene, tetrahydrofuran, dichloromethane, 1,2-dichloroethane, monochlorobenzene, ethyl acetate, butyl acetate, cyclohexanone, methanol, butanol, and the like are singly used or used in combination thereof.
A photosensitive layer coating process in the immersion coating is performed such that as the hollow cylinder is vertically immersed into the liquefied photosensitive solution and then taken out therefrom, the liquefied photosensitive solution is applied on the surface of the hollow cylinder to form a wet-coated film, and then the solvent is evaporated from the applied photosensitive solution wet-coated film and dried to be cured to form the photosensitive layer.
Meanwhile, since the immersion coating method is performed in the vertical direction, the applied photosensitive solution may flow downward due to gravitational influence to generate deviation in coating amount between upper and the lower portions. Although the amount of the photosensitive solution is sometimes insufficient not to flow downward, when the solvent is evaporated form the coated photosensitive solution wet-coated film, deviation in photosensitive solution density of the wet-coated film may be generated, a convection phenomenon may be generated, and as a result, a problem of a spot shape in which the deviation in coating amount is generated by positions may be generated.
When the deviation in the coating amount occurs irregularly in positions and upper and lower portions of the photosensitive layer over an entire area of the photosensitive drum, image deviation having the same shape of the coating amount deviation is generated in a printed image, and thus uniform coating of the photosensitive layer is very important in quality of the photosensitive body. In particular, in a color printer mixing four colors to express an image, a problem caused by the deviation in photosensitive layer coating amount is further serious because it generates color distortion in addition to a simple image density deviation in comparison with a mono printer using a single color. To solve the above-described problem, a quick drying solution of the photosensitive material should be prepared so that the wet-coated film formed on the surface of the hollow cylinder during the immersion coating is not flown downward or the spot is not generated and quickly dried.
Since an evaporation speed of the used solvent is considered to prepare the quick-drying photosensitive solution, the evaporation speed of the solvent is generally expressed as a relative evaporation speed by calculating, on the basis of time required for evaporating ether of 1, time required for evaporating the same amount of different solvent. Among various kinds of solvents used as the photosensitive solution, since toluene having the relative evaporation speed of 6.1, monochlorobenzene having the relative evaporation speed of approximately 10, or butyl acetate having the relative evaporation speed of 11 have the slow evaporation speed, as curing thereof has slowly progressed to lengthen time for staying as a liquid state of an uncured state on the outer surface of the hollow cylinder, the amount flowing downward is great to generate great deviation in upper and lower portions of the thickness of the coated film of the photosensitive drum cylinder, or as the convection phenomenon is continued while the wet-coated film state is maintained for a long time to easily generate the spot, the solvent may not be singly used and thus used as a solvent added to retard the evaporation speed of other solvents. On the other hand, in case of dichloromethane, since it has very fast relative evaporation speed of 1.8, it is favorable in terms of reducing deviation in the photosensitive layer coating amount of the photosensitive drum cylinder. However, since density of the inputted photosensitive solution extremely increases because rapid evaporation of the solvent is continued while processing the process, difference in the coating amounts between the initially produced photosensitive drum cylinder and latter produced photosensitive drum cylinder during production is generated. When the solvents such as tetrahydrofuran (relative evaporation speed of 2.3), 1,2-dichloroethane (relative evaporation speed of 2.7), ethyl acetate (relative evaporation speed of 3), or the like is used as a main solvent, since it effectively reduces the deviation in coating amount according to the upper and lower portions and positions of the photosensitive drum cylinder and has volatility enabling the density of the photosensitive solution not to be greatly changed, it may be used as the main solvent. Alternatively, the dichloromethane having the very fast relative evaporation speed is mixed with toluene, monochlorobenzene, or the like, which has very slow relative evaporation speed, to have the appropriate evaporation speed, thereby being used as the main solvent.
In this case, referring to FIG. 1, when a hollow cylinder 20 is immersed into a photosensitive solution 30 for immersion coating, a sealed space 40 is defined between a gripping mechanism 120 and a liquid surface of the photosensitive solution in the hollow cylinder 20, and high volatile solvents are fast evaporated to be diffused into the sealed space 40 so that evaporation vapor increases a total gas volume in the sealed space 40. The above-described solvent evaporation on a liquid surface at a lower portion of the sealed space 40 is continued until the sealed space 40 is saturated by the vapor of the corresponding solvent, and thus the volume of the gas of the vapor element of the newly generated solvent pushes the liquid surface at the lower end of the hollow cylinder 20 to be downward protruded, and bubbles are eventually discharged toward the photosensitive solution 30. The discharged bubbles float from the lower end of the hollow cylinder 20 up to the liquid surface of an upper portion of the photosensitive solution 30, and are taken out to be attached to the outer surface of the hollow cylinder 20 and broken-up, so that the bubble break-up is marked in a bubble break-up region of the coated film to generate a defect.
To improve the above-described problem, provided is a method in which a hole for discharging air is defined in the gripping mechanism 120 to discharge a predetermined amount of inner air to the outside while the hollow cylinder 20 is immersed into the photosensitive solution 30 in a state the hollow cylinder 20 is gripped by the gripping mechanism in an initial coating process, and the photosensitive solution 30 is introduced into the hollow cylinder 20 as many as the volume of the discharged air to raise the liquid surface of the photosensitive solution 30 by a predetermined distance from the lower end of the hollow cylinder 20 (refer to FIG. 2). In this case, although the solvent is rapidly evaporated from the liquid surface raised by a predetermined distance from the lower end of the hollow cylinder 20 in the coating process, the liquid surface is lowered only as many as the volume increased due to the generated solvent vapor, and the bubbles are not discharged to the external photosensitive solution 30 outside the hollow cylinder. As a result, as the photosensitive solution 30 prepared by using the solvent having the fast evaporation speed is used, the photosensitive drum having the small deviation in photosensitive coating amount may be manufactured. However, in the above-described method, the manufacturing cost increases because the high-priced photosensitive solution 30 is unnecessarily applied to the inner surface as well as the outer surface, which is a functional part of a product, of the hollow cylinder 20.
The applying of the photosensitive material to the inner surface of the photosensitive drum has another problem as follows in addition to the cost increase problem. A gear or a bearing element including a grounding electrode is assembled to an inner surface of both ends or one side end of the photosensitive drum to which the coating of the photosensitive layer is completed in a press-fit method. Since the press-fit assembly is impossible when the photosensitive layer is applied on the inner surface, the photosensitive layer of the unnecessarily coated inner surface needs to be wiped out by using a sponge or a brush immersed into an organic solvent, and thus additional process is added to thereby increase the manufacturing cost. In addition to the problem in the manufacturing process, in the photosensitive drum manufactured by the related art method, since the coating layer of the inner surface is not easily and completely removed by the wiping process, degree of precision in assembling parts such as the gear and the bearing element may be affected, and thus a problem may occur in terms of mechanical element quality such as the runout tolerance of the photosensitive drum. Since the runout tolerance of the photosensitive drum directly affects an amount of toner transferred from a developing roller to a photosensitive drum, when the runout tolerance of the photosensitive drum is over regulatory criteria, nonuniformity of an image may be seriously generated.